From 2b235765e9d4426cf56d7fd1a331f81a4dbbd85a Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 25 Sep 2025 22:49:14 +0000 Subject: [PATCH] scm: use masked_user_access_begin() in put_cmsg() Use the greatest and latest uaccess construct to get an optimal code. Before : lea (%r9,%rcx,1),%r10 movabs $,%r11 mov $0xfffffff2,%eax cmp %rcx,%r10 jb ffffffff81cdc312 cmp %r11,%r10 ja ffffffff81cdc312 stac lfence mov %r9,(%rcx) After: movabs $,%r9 cmp %r9,%rax cmova %r9,%rax stac mov %rcx,(%rax) Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20250925224914.3590290-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/core/scm.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/core/scm.c b/net/core/scm.c index 072d5742440a..66eaee783e8b 100644 --- a/net/core/scm.c +++ b/net/core/scm.c @@ -273,7 +273,9 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data) check_object_size(data, cmlen - sizeof(*cm), true); - if (!user_write_access_begin(cm, cmlen)) + if (can_do_masked_user_access()) + cm = masked_user_access_begin(cm); + else if (!user_write_access_begin(cm, cmlen)) goto efault; unsafe_put_user(cmlen, &cm->cmsg_len, efault_end); -- 2.51.0